When the hydrostatic weight of the column of mud in a well bore is less than the formation pressure, the potential for a blowout exists. A blowout occurs when the formation expels hydrocarbons into the well bore. The expulsion of hydrocarbons into the well bore dramatically increases the pressure within a section of the well bore. The increase in pressure sends a pressure wave up the well bore to the surface. The pressure wave can damage the equipment that maintains the pressure within the well bore. In addition to the pressure wave, the hydrocarbons travel up the well bore because the hydrocarbons are less dense than the mud. If the hydrocarbons reach the surface and exit the well bore through the damaged surface equipment, there is a high probability that the hydrocarbons will be ignited by the drilling or production equipment operating at the surface. The ignition of the hydrocarbons produces an explosion and/or fire that is dangerous for the drilling operators. In order to minimize the risk of blowouts, drilling rigs are required to employ a plurality of different pressure control devices, such as an annular pressure control device, a pipe ram pressure control device, and a blind ram pressure control device. If a “closed loop drilling” method is used, then a rotating pressure control device will be added on top of the conventional pressure control stack. Persons of ordinary skill in the art are aware of other types of pressure control devices. The various pressure control devices are positioned on top of one another, along with any other necessary surface connections, such as the choke and kill lines for managed pressure drilling applications and nitrogen injection lines for under balanced drilling applications. The stack of pressure control devices and surface connections is called the pressure control stack.
One of the devices in the pressure control stack can be a rotating pressure control device also referred to as a rotating pressure control head. The rotating pressure control head is located at the top of the pressure control stack and is part of the pressure boundary between the well bore pressure and atmospheric pressure. The rotating pressure control head creates the pressure boundary by employing a ring-shaped rubber or urethane sealing element that squeezes against the drill pipe, tubing, casing, or other cylindrical members (hereinafter, drill pipe). The sealing element allows the drill pipe to be inserted into and removed from the well bore while maintaining the pressure differential between the well bore pressure and atmospheric pressure. The sealing element may be shaped such that the sealing element uses the well bore pressure to squeeze the drill pipe or other cylindrical member. However, some rotating pressure control heads utilize some type of mechanism, typically hydraulic fluid, to apply additional pressure to the outside of the sealing element. The additional pressure on the sealing element allows the rotating pressure control head to be used for higher well bore pressures.
The sealing element on all rotating pressure control heads eventually wear out because of friction caused by the rotation and/or reciprocation of the drill pipe. Additionally, the passage of pipe joints, down hole tools, and drill bits through the rotating pressure control head causes the sealing element to expand and contract repeatedly, which also causes the sealing element to become worn. Other factors may also cause wear of the sealing element, such as extreme temperatures, dirt and debris, and rough handling. When the sealing element becomes sufficiently worn, it must be replaced. If a worn sealing element is not replaced, it may rupture, causing a loss of hydraulic fluids and control over the well head pressure.
Currently, visual inspections or time based life span estimates are used to determine when to replace a worn sealing element. Visual inspections are subjective, and may be unreliable. Time based estimates may not take into account actual operating conditions, and be either too short or too long for a particular situation. If the time based estimate is too conservative, then sealing elements are replaced too frequently, causing unnecessary expense and delay. If the time based estimate is too aggressive, then the risk for rupture may be unacceptable.
U.S. patent application Ser. No. 10/922,029 (the '029 application) discloses a Rotating Pressure Control Head (RPCH) having a sealing element in an inner housing where the inner housing is rotatably engaged to an outer housing by an upper bearing and a lower bearing. The RPCH of the '029 application offers many improvements over the prior art including a shorter stack size, a quick release mechanism for inner unit change out, and a reduction in harmonic vibrations. Further improvements can be sought in ways to extend the life of the components. Wellbore fluid pressure, pressurized hydraulic fluid, and pipe friction against the sealing element exert a net upward or downward force on the inner housing that translates into a load on the upper and lower bearings. The load on the upper and lower bearings generates heat which is the most significant factor in bearing wear and life expectancy. A need exists for a way to balance the net force on the inner housing in order to reduce heat and wear on the bearings. Additionally, a need exists for an objective way to determine when a sealing element is sufficiently worn and needs to be replaced, without causing waste from early replacement, and without increasing the risk of rupture.